The present invention provides improved compositions and methods for enhancing fluid flow from a subterranean formation. In preferred embodiments, the present invention provides compositions and methods for enhancing subterranean well productivity by enhancing fracture conductivity.
Hydraulic fracturing is a technique for stimulating the production of a subterranean formation. The technique generally involves injecting a viscous liquid through a well bore into a portion of a subterranean formation at a chosen rate and pressure to overcome the formation's stresses and form or enhance a fracture in the formation; and placing proppant particulates in the fracture to, among other things, maintain the fracture in a propped condition when the injection pressure is released. The resultant propped fracture provides a conductive channel in the formation for fluids to flow to the well bore.
The degree of stimulation afforded by the hydraulic fracture treatment is largely dependent on the permeability and width of the propped fracture. Thus, the productivity of the well, in effect, becomes a function of fracture conductivity. To enhance well productivity, it may be necessary to enhance fracture conductivity.
Oftentimes, to effectively prop open the fractures as well as to prevent proppant particulate flow back, the proppant particulates are caused to consolidate within the fractures. One conventional means of doing this is to use resin-coated proppant particulates so that when the resin cures, the proppant particulates can consolidate into a mass within the fractures.
Although consolidating the proppant particulates within a fracture may have some benefits, for example, preventing proppant particulate flow back, such methods may adversely affect the conductivity of the fracture. That is, some methods of consolidating proppant particulates themselves may introduce a barrier to the free flow of fluids from the subterranean formation to the well bore for subsequent production. Fracture conductivity may suffer as a result. This is undesirable as this may affect overall well productivity.
To counteract this potential problem, many different techniques have been developed. One technique involves adding calcium carbonate or salt to the proppant composition. Once the proppant particulates have substantially consolidated, the carbonate or salt dissolves. At least one problem associated with this method is the incomplete removal of the carbonate or salt if not adequately contacted with a fluid capable of dissolving the carbonate or salt. Another method has been to add wax particulates to the proppant composition. Once incorporated into the consolidated proppant particulates, the wax particulates may melt as a result of the temperature of the formation. A problem with this method is that the wax has been known to resolidify in the well, causing a multitude of problems. Another method that has been used is to add an oil-soluble resin to the proppant composition; however, this method has not been successful because of, among other things, nonuniform placement of the particles.
Another way to address fracture conductivity and proppant matrix permeability has been to use bigger proppant particulates. However, there are practical limits to the size of the proppant that may be used. For instance, if overly large particles are used, premature screen out at the perforations and/or fractures during the proppant stage of fracturing treatment often occurs as large size proppant particulates are injected into the fractures. In addition, by using overly large proppant particles, the ability to control formation sand may be lost as the formation sand or fines tend to invade or penetrate the large pore space of the proppant pack during production of hydrocarbons, thus choking the flow paths of the fluids.